The top band abruptly rushed in and touched just below
Ranma's left eye, forming a glowing triangle. The
bottom band of light repeated the effect for the right
eye. The remaining band swirled for a few seconds more,
and then rushed in to touch the center of her forehead,
forming an upright infinity symbol. Ranma jerked and
strained even harder at the last contact.

I have not read all of Aa! Megami-sama, however, the parts I have 
read all showed the same markings on the forehead as on the 
cheeks.  Unless there is something very different about Ranma 
should he not have the same markings in both places?

Not quite true...
    Belldandy has a triangle on each cheek and an elongated diamond 
    on her forehead.
At first I was convinced that different marks on cheeks and forehead
marked first class goddesses but the fact that Peorth has the same
mark(diamond) on both cheeks and forehead makes me cautious.

Who can come up with any explanation for goddess' markings?

    May the Gods protect thee from Carpal-tunnel,
    Arjuna.